Treatment of solutions of nonylphenol (NP), Triton X-100 (TrX) and phenol in a flow-through undivided EC reactor equipped with a Co(2+)-promoted PbO(2) anode and a stainless steel cathode was accompanied by consistent changes of absorbance, fluorescence and mass spectra of the effluents, and formation of aldehydes ranging from formaldehyde to decyl aldehyde. Deconvolution of the absorbance spectra of EC-treated NP, TrX and phenol and examination of their fluorescence indicated that the compounds are rapidly degraded in the reactor. For NP, the degradation of the target proceeded via the generation (at current densities <25mA/cm(2)) of benzoquinone intermediates that yielded peaks with m/z ratios 223, 227, 235, and 241D in the mass spectra. Their breakdown at current densities >10mA/cm(2) was accompanied by the release of aldehydes that were predominated by acetaldehyde and formaldehyde. The total yield of aldehydes increased with the current density, but their speciation showed little sensitivity to it. Deconvolution of the absorbance spectra of NP solutions subjected to ozonation, and analysis for reaction by-products formed in these conditions showed the reaction pathway in the latter case was likely to be similar to that observed for the EC treatment.